This research project is directed toward analysis of the nature of the morphogenetic field of the regenerating amphibian limb, and the mechanism whereby it respecifies new spatial patterns of cell differentiation. The general hypothesis is that the morphogenetic field is an outline of what is to be regenerated. The outline consists of cellular boundary properties which are asymmetrically distributed among the mesodermal cells on the limb circumference and along the proximal-distal (PD) axis. Specific hypotheses to be tested are (1) there are both continuous limb gradients and homologous, segmentally repeating gradients of morphogenetic information along the PD axis of the limb; (2) the proximal boundary of the outline is determined by level-specific cell properties which allow only distal transformation; and (3) the axial organization of the morphogenetic field is autonomous and cannot be altered by extracellular or cell-associated signals from adjacent differentiated stump tissues.